1. Field of the Invention
The invention relates to binary data transmission with redundance reduction.
2. Description of the State of the Art
It is desired for the transmission of binary-coded picture information to save transmission time and band width by using a coding with the help of which the rendundance is reduced which is present in the picture information supplied by the sensor. For this purpose, the so-called run-time coding has been stated in the past, whereby the information of each picture dot is not individually transmitted, but continuous run-lengths of equal information (runs) are transmitted as longitudinally coded digital values (U.S. Pat. No. 2 922 840).
The run-length coding has been improved in the meantime by Huffman in such a way that the coding of the transit lengths is effected with code words of different lengths. The run lengths occurring most often are occupied by the shorter code words, and the run lengths occurring less often are occupied with longer code words, depending on the probability of their occurrence in the picture. With this type of coding, an optimum code can be found, but the electronic expense for the coding and decoding of long code words, which occur seldom but which do occur, cannot be incurred.
As an improvement, a so-called broken Huffman-Code has been described in "IEE International Convention Record" of P. D. Dodd and F. B. Wood, 1963, Pages 60 to 93, whereby the Huffman coding is carried out up to a justifiable run-length. For larger run-lengths, a prefix word with a subsequent code word of constant length with n bits is introduced which states the actual run-length as a binary number. This code has also been stated by W. S. Michel, W. O. Fleckenstein and E. R. Kretzmer in "Wescon Convention Record", 1957, Part 2, Vol. 1, Pages 84 to 93. Thus, a good redundance reaction can be obtained, but the code is very susceptible to disturbance, and a disturbance, which has occurred once, will be carried from line to line, since the decoder does not recognize it.